Three-phase motors have been widely used; an example of these three-phase motors is disclosed in Japanese Patent Application Publication No. 2003-333785.
FIG. 28 is an axial cross sectional view schematically illustrating a typical structure of such a three-phase motor.
The motor illustrated in FIG. 28 is provided with an output shaft 511, a substantially annular rotor core 512, and a pair of N and S poles 517 and 518 of permanent magnets. The motor is also provided with a pair of bearings 513, a substantially annular stator core 514, and a substantially cylindrical inner hollow motor housing 516 with an opening in its axial direction.
The output shaft 511 is fixedly mounted on an inner circumference of the rotor core 512. The output shaft 511 is disposed in the opening of the motor housing 516 such that both ends thereof project from the opening, and the rotor core 512 is installed in the motor housing 516. The output shaft 511 is rotatably supported by the motor housing 516 with the bearings 513. The N and S poles 517 and 518 are, for example, mounted on the outer circumference of the rotor core 512 such that the N and S poles are alternatively arranged in the circumferential direction of the rotor core 512. The rotor core 512 and the N and S poles 517 and 518 of the permanent magnet constitute a rotor of the motor.
The stator core 514 is installed in the motor housing 516 such that its inner circumference is opposite to the outer circumference of the rotor core 512 with an air gap therebetween. Three-phase stator windings are installed in the stator core 514. Ends 515 of the three-phase stator windings are drawn out from the stator core 514. The three-phase stator windings and the stator core constitute a stator.
FIG. 29 is a lateral cross sectional view taken on line AA-AA in FIG. 28. In these FIGS. 28 and 29, a two-pole, 12-slot three-phase motor is used. In order to simply illustrate the structure of the motor, hatching of the motor is omitted in illustration in FIG. 29.
As each of the three-phase stator windings of the three-phase motor illustrated in FIGS. 28 and 29, a distributed, full pitch winding is used. In FIG. 29, the stator core 514 consists of an annular back yoke and 12 teeth projecting inwardly and circumferentially arranged at equal pitches therebetween. Spaces between circumferentially adjacent teeth provide 12 slots of the stator core 514; these spaces provide slots 563 (563a to 563l) of the stator core 514. U-, V-, and W-phase stator windings are distributedly arranged.
Specifically, a first U-phase winding 521, 528 is wound from a slot 563a to another slot 563f via one axial end of the stator core 514, and a second U-phase winding 522, 527 is wound from a slot 563l to another slot 563g through one axial end of the stator core 514. These first and second U-phase windings 521, 528 and 522, 527 are electromagnetically wound in parallel to each other.
A first V-phase winding 525, 52C is wound from a slot 563i to another slot 563b through one axial end of the stator core 514, and a second V-phase winding 526, 52B is wound from a slot 563h to another slot 563C through one axial end of the stator core 514. These first and second V-phase windings 525, 52C and 526, 52B are electromagnetically wound in parallel to each other.
A first W-phase winding 529, 524 is wound from a slot 563e to another slot 563j through one axial end of the stator core 514, and a second W-phase winding 52A, 523 is wound from a slot 563d to another slot 563K through one axial end of the stator core 514. These first and second W-phase windings 529, 524 and 52A, 523 are electromagnetically wound in parallel to each other.
FIG. 30 schematically illustrates, in enlarged scale, a part of the motor illustrated in FIG. 29; this part encloses some slots 563. Reference numeral 562 represents the teeth, and reference numeral 565 represents insulating papers as an example of insulating members inserted in corresponding slots 563.
A group of conductors in one-phase winding contained in a corresponding one slot 563 is represented in FIG. 30 by reference numeral 564. In other words, the number of conductors in one-phase winding contained in a corresponding one slot represents the number of turns of the one-phase winding through the corresponding one slot.
Three-phase inverters are normally used to apply a sinusoidal voltage as a fundamental wave to each of the three-phase windings to thereby generate a rotating field. The rotating field turns the rotor based on magnetic actions between the rotating field and the N and S poles.
However, these three-phase inverters may create the fifth and seventh harmonic voltage contents of the fundamental wave; these fifth and seventh harmonic voltage contents may cause the sixth harmonic torque contents to appear in a torque of three-phase motors to be driven.
Next, FIG. 31 schematically illustrates, as an example of five-phase motors, a two-pole, 10-slot five-phase motor. In order to simply illustrate the structure of the motor, hatching of the motor is omitted in illustration in FIG. 31.
In FIG. 31, a stator core 53D of a stator of the motor includes an annular back yoke and ten teeth projecting inwardly and circumferentially arranged at equal pitches therebetween. Spaces between circumferentially adjacent teeth provide ten slots of the stator core 53D; these spaces provide slots 530 (530a to 530j) of the stator core 53D.
The stator is made up of five-phase stator windings. As each of the five-phase stator windings, a concentrated, full pitch winding is used.
Specifically, an A-phase winding 531 and 536 is concentrically wound in a slot 530a and in a slot 530f through one axial end of the stator core 53D at a pitch of 180 electrical degrees.
A B-phase winding 533 and 538 is concentrically wound in a slot 530i and in a slot 530d though one axial end of the stator core at a pitch of 180 electrical degrees. A C-phase winding 535 and 53A is concentrically wound in a slot 530g and in a slot 530b though one axial end of the stator core at a pitch of 180 electrical degrees.
A D-phase winding 537 and 532 is concentrically wound in a slot 530e and in a slot 530j through one axial end of the stator core 53D at a pitch of 180 electrical degrees. An E-phase winding 539 and 534 is concentrically wound in a slot 530c and in a slot 530h though one axial end of the stator core at a pitch of 180 electrical degrees.
The pitch of each of the A-, B-, C-, D-, and E-phase windings corresponds to one pole pitch (180 electrical degrees) of a rotor of the motor. That is, ten slots are circumferentially disposed within an angular range of 360 electrical degrees of the stator; this angular range corresponds to two-pole pitch (one north-pole pitch or one south-pole pitch) of the rotor.
FIG. 32 schematically illustrates, as another example of five-phase motors, a four-pole, 10-slot five-phase motor. In order to simply illustrate the structure of the motor, hatching of the motor is omitted in illustration in FIG. 32.
In FIG. 32, a stator core 54B of a stator of the motor includes an annular back yoke and ten teeth projecting inwardly and circumferentially arranged at equal pitches therebetween. Spaces between circumferentially adjacent teeth provide ten slots of the stator core 54B; these spaces provide slots of the stator core 54B. The stator core 54B is made up of a plurality of magnetic steel sheets stacked in alignment.
The stator is made up of five-phase stator windings. As each of the five-phase stator windings, a concentrated, short pitch winding is used.
Specifically, a first A-phase winding 540 and 541 is concentrically wound around one tooth 54E in corresponding circumferentially adjacent slots, and a second A-phase winding 546 is concentrically wound around one tooth in corresponding circumferentially adjacent slots. The first A-phase winding 540 and 541 and the second A-phase winding 546 are connected to each other in series; these windings form an A-phase winding 551 (see FIG. 33). As illustrated in FIG. 33, the motor is designed to cause a current IA to flow through the A-phase winding 551.
A first B-phase winding 542 and 54F is concentrically wound around one tooth in corresponding circumferentially adjacent slots, and a second B-phase winding 547 is concentrically wound around one tooth in corresponding circumferentially adjacent slots. The first B-phase winding 542 and 54F and the second B-phase winding 547 are connected to each other in series; these coils form a B-phase winding 552 (see FIG. 33). As illustrated in FIG. 33, the motor is designed to cause a current IB to flow through the B-phase winding 552.
A first C-phase winding 543 is concentrically wound around one tooth in corresponding circumferentially adjacent slots, and a second C-phase winding 548 is concentrically wound around one tooth in corresponding circumferentially adjacent slots. The first C-phase winding 543 and the second C-phase winding 548 are connected to each other in series; these coils form a C-phase winding 553 (see FIG. 33). As illustrated in FIG. 33, the motor is designed to cause a current IC to flow through the C-phase winding 553.
A first D-phase winding 544 is concentrically wound around one tooth in corresponding circumferentially adjacent slots, and a second D-phase winding 549 is concentrically wound around one tooth in corresponding circumferentially adjacent slots. The first D-phase winding 544 and the second D-phase winding 549 are connected to each other in series; these coils form a D-phase winding 554 (see FIG. 33). As illustrated in FIG. 33, the motor is designed to cause a current ID to flow through the D-phase winding 554.
A first E-phase winding 545 is concentrically wound around one tooth in corresponding circumferentially adjacent slots, and a second E-phase winding 54A is concentrically wound around one tooth in corresponding circumferentially adjacent slots. The first E-phase winding 545 and the second E-phase winding 54A are connected to each other in series; these coils form an E-phase winding 555 (see FIG. 33). As illustrated in FIG. 33, the motor is designed to cause a current IE to flow through the E-phase winding 555.
These currents IA, IB, IC, ID, and IE represent five-phase currents, and these A-, B-, C-, D-, and E-phase windings 551, 552, 553, 554, and 555 constitute a stator coil. In FIG. 32, reference numeral 54C represents a pair of two opposing salient north poles of a rotor, and reference numeral 54D represents a pair of two opposing salient south poles of the rotor.
As well as the five-phase motor illustrated in FIG. 31, ten slots are circumferentially disposed within an angular range of 360 electrical degrees of the stator core 54B; this angular range corresponds to two-pole pitch (one north-pole pitch or one south-pole pitch) of the rotor.
Each of the first and second windings for each phase is concentrically wound around a corresponding one tooth. For this reason, in comparison to the structure of the five-phase motor illustrated in FIG. 31, it is possible to more easily manufacture the stator (motor), to increase the winding space factor of each phase winding, and to shorten the length of the axial end of each of the stator coils of the motor. Note that the winding space factor of one-phase winding installed in one slot represents the ratio of the total cross-sectional area of the turns in the one slot to the cross-sectional area of the one slot.